Malaria, caused by a parasitic protozoan called Plasmodium, is one of the most serious and complex tropical parasitic diseases. Generally human malaria is caused by four species of malarial parasites which are Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale and Plasmodium malariae. Of these P. falciparum and P. vivax are most widespread and cause most of the mortality and morbidity associated with these types of infections.
It is known that the material parasites undergo complex life cycle in humans, which is initiated through the bite of an infected female Anopheles mosquito. When the mosquito bites a host, some of the sporozoites are injected into the bloodstream of the host and through the circulation they reach the liver where they multiply and liberate merozoites into the bloodstream which then invade the erythrocytes. In case of infections caused by P. vivax, most of the time the parasites remain dormant in the liver which stage is termed hypnozoites. Hypnozoites are reactivated and reinitiate blood stage parasitemias causing relapse. It has often been observed that people infected with P. vivax do not experience any symptoms for a very lone period after their initial illness but become symptomatic after certain period (Korean J. Intern Med, 1999 Jul; 14(2): 86-9).
A number of drugs ranging from those of natural origin to synthetic ones have been developed for the treatment of malaria. Quinine and artemisinin are the commonly know drugs of natural origin, which are mostly used for the treatment of malaria. A number of synthetic anti-malarial drugs such as chloroquine, mefloquine, primaquine, halofantrine, amodiaquine, proguanil, maloprim are known in the literature. Of all the synthetic anti-malarial agents chloroquine has been the most widely prescribed drug for the treatment of malaria of all the types, for more than last 60 years.
Chloroquine has been the effective treatment so far for the P. vivax malarial infections, however, some strains of P. vivax have shown resistance to this well known drug (Ann. Trop. Med. Parasitol., 1999 Apr; 93(3): 225-230). In recent years drug resistant malaria has become one of the most serious problems in malaria control. Drug resistance necessitates the use of drugs which are more expensive and may have dangerous side effects. To overcome the problems associated with drug resistance, treatments comprising combinations of anti-malarial agents are on the rise. A number of anti-malarial combinations are already known in the malarial chemotherapy. For example, a combination of amodiaquine and tetracycline, a combination of sulfadoxine and pyrimethamine known as fansidar, are known therapies for the treatment of P. falciparum. Also fansimef, a combination of mefloquine with sulfadoxine and pyrimethamine is used against multidrug resistant strains of P. falciparum. 
U.S. Pat. No. 5,998,449 describes a method for the treatment of malaria wherein combination of atovaquone and proguanil is used for the treatment of malaria. In U.S. Pat. No. 5,834,505, combination of fenozan with another anti-malarial agent selected from artemisinin, sodium artesunate, chloroquine, mefloquine is described for the prophylactic and curative treatment of malaria.
All the aforementioned anti-malarial combinations reported heretofore are generally used for the treatment of P. falciparum. None of the standard anti-malarial combination treatment regimens have been found to be favourable for the treatment of P. vivax malaria which is the most relapsing type of malaria. For a very long time chloroquine was used for the treatment of infections caused by P. vivax, however, chloroquine eradicates only the asexual erythrocytic stages of P. vivax and does not eliminate the hypnozoites. Until recently primaquine has been the drug of choice for the treatment of malarial relapse. Generally the standard therapy for the P. vivax malarial infection comprises of a sequential chloroquine-primaquine combination treatment regimen wherein primaquine is administered for 14 days following the 3 days course of chloroquine. WHO (World Health Organisation) also recommends a 14 days primaquine treatment for P. vivax malarial infection. A shorter duration of chloroquine-primaquine treatment regimen was also tried out wherein primaquine was administered only for 5 days following the chloroquine course. However, the outcome of the treatment was not encouraging, since the percentage relapse was more than the standard 14 days primaquine treatment regimen (Trans. R. Soc. Trop. Med. Hyg., 93(6), 641-643). Also primaquine is known to cause hemolytic anemia in persons deficient in the enzyme glucose-6-phosphate dehydrogenase (G6PD) (Pharmacol Rev. 21: 73-103 (1969); Rev. Cubana Med trop, 1997; 49 (2):136-8). Moreover, methemoglobin toxicity is another predictable does-related adverse effect associated with primaquine. Needless to say that in the case of sequential combination therapy the patient may not complete the course once the symptoms of malaria are diminished, hence this may increase the chances of relapse. Thus, the chloroquine-primaquine treatment regimen is not safe with respect to toxicity of primaquine and has a further limitation from the standpoint of patient compliance due to longer duration of treatment.
Another anti-relapse agent namely tafenoquine is disclosed in U.S. Pat. No. 4,617,394. Though more effective than primaquine, the drug was found to cause methemoglobin toxicity almost three times more than that of primaquine (Fundam. Appl. Toxicol. 1988, 10(2), 270-275), hence has drawbacks in terms of safety.
The compound, 3-[1-[[4-[(6-methoxy-8-quinolinyl)amino]pentyl]amino]-ethylidene]-dihydro-2(3H)furanone is a derivative of primaquine. It was described in Indian Patent Specification No. 158111 as 6-methoxy-8-(4-N-(3′-aceto-4′,5′-dihydro-2-furanylamino)-1-methylbutylamino)quinoline, the structure of which was revised to that represented by the following formula I. As per the revised structure, the compound is named 3-[1-[[4-[(6-methoxy-8-quinolinyl)amino]pentyl]amino]ethylidene]-dihydro-2(3H)-furanone (hereinafter referred to as compound I). The revised structure is described in WHO Drug Information Vol. 13, No. 4, pg. 268 (1999).

The compound of formula (I) has been found to be safer and less toxic than the present compound primaquine (Am. J. Trop. Med. Hyg, 1989 Dec.; 41(6): 635-637). Its anti-relapse activity has been found to be comparable to primaquine.
Over the years primaquine was the only drug used for the radical cure of malaria caused by P. vivax. Primaquine is associated with a number of severe adverse effects, therefore there is a need to develop agents which are more effective and/or less toxic than primaquine. The compound I has been found to exhibit anti-relapse activity comparable to Primaquine (Am. J. Trop. Med. Hyg., 41(6): 633-637 (1989)). However, this compound has been shown to cause less methemoglobin formation (Am. J. Trop Hyg., 41(6): 638-642 (1989)) and also has less effect on anti-oxidant defense enzymes than primaquine (Biochem Pharmacol. 46(10):1859-1860 (1993)). Thus, this primaquine derivative (I) is found to be less toxic as compared to the parent drug, primaquine.
Therefore, there is a longfelt need for a more practical, effective, patient compliant and safe remedy for the radical cure of P. vivax malarial infection.
The inventors have found that the longfelt need may be fulfilled by providing a treatment regimen consisting of regulated use of chloroquine and 3-[1-[[4-[(6-methoxy-8-quinolinyl)amino]pentyl]amino]ethylidene]-dihydro-2(3H)furanone of formula I over a period of between 5 to 8 days.
It has also been found that the treatment regimen may be executed most effectively and in a user friendly manner by providing a combination kit which comprises two anti-malarial agents, namely chloroquine and 3-[1-[[4-[(6-methoxy-8-quinolinyl)amino]pentyl]amino]ethylidene]-dihydro-2(3H)furanone and an instruction material containing instructions for the administration of two anti-malarial agents during the period of treatment.
Thus the present invention relates to a combination kit for the treatment of P. vivax malaria for a period of between 5 to 8 days which comprises                a) a predetermined dose of a first anti-malarial agent namely chloroquine;        b) predetermined dose of second anti-malarial agent namely 3-[1-[[4-[(6-methoxy-8-quinolinyl)amino]pentyl]amino]-ethylidene]-dihydro-2(3H)furanone;        c) an instruction manual containing instructions for administering the two anti-malarial agents during the treatment period.        
The present invention also relates to a method for producing a combination kit for the treatment of P. vivax malaria for a period of between 5 to 8 days which comprises:                a) providing a predetermined dose of a first anti-malarial agent namely chloroquine;        b) providing a predetermined dose of second anti-malarial agent namely 3-[1-[[4-[(6-methoxy-8-quinolinyl)amino]pentyl]-amino]ethylidene]-dihydro-2(3H)furanone;        c) providing an instruction manual containing instructions for administering the two anti-malarial agents during the treatment period.        
The present invention further relates to a method of treatment of malaria caused by P. vivax comprising administering a first anti-malarial agent, chloroquine and a second anti-malarial agent, 3-[1-[[4-[(6-methoxy-8-quinolinyl)amino]pentyl]amino]ethylidene]-dihydro-2(3H)furanone in predetermined doses and in a predetermined sequence for a period of between 5 to 8 days.